Ph.D. on community responses to climate change

This Ph.D. project was commenced in June 2006 by Ph.D. student Jane Kongstad Pedersen. The project is mainly linked to the WP3.1 and will focus on the effects of increased CO₂ concentration, increased temperature and changes in precipitations on the plant phenology, biomass and species composition. 

The study seeks to investigate how predicted climate changes will affect the seasonal and the long term variations in the structure and dynamics of the vegetation. Furthermore it will describe the plant responses with regard to acclimations, tolerance and recovering after extreme climatic events.

The aim of this project is to describe the plant responses, both on individual and community level, to the predicted climate change scenarios.

Methods will include repeated pin-point analysis in order to describe variation in species composition, cover and compactness and the phenology of the two dominant species, Calluna vulgaris and Deschampsia flexuosa, over the season and from year to year. This method will furthermore allow conversion to biomass estimates.

Individual plants will be marked and followed, and bud burst, shoot elongation, senescence and the number of active meristems will be registered.

The vegetation greenness indicator, NDVI will be measured in order to describe seasonal variations in plant cover and biomass, as well as mortality and leaf appearance.  

Background
Changes in the climatic factors temperature, CO₂ and precipitation will most likely affect plant phenology and composition and may thereby affect many processes in the ecosystem.

The increased temperature can lead to a longer growing season and a higher rate of mineralization during the spring and the autumn. During the summer the predicted decrease in precipitation will lead to a longer drought period. 

Changes in these conditions is thought to affect the phenogical cyclus of the plants such as flowering time, shoot length, daughter shoot production, leaf appearance and mortality. The responses to the changes will likely be different from species to species, and changes in the climate will therefore lead to changes in plant compositions.

A larger pool of available nutrients due to a higher rate of mineralization, will lead to out-competition of the species tolerant to low nutrient levels (e.g. Calluna vulgaris) and favour the fast growing and more nutrient demanding species (e.g grasses and herbs). These species have higher nutrient contents, which may lead to changes in litter chemistry and subsequently a lower nutrient turn over time and thereby make the pool of available nutrients even larger. Together these effects may lead to an increase in the primary production of the ecosystem.   

The changes in species composition may favour the graminoid Deschampsia flexuosa proportional to the ecicoid dwarf shrub Calluna vulgaris. Due to the different life strategies, different nutrient demands and the different competitive capacity of the two species, the changes from heather to grass would lead not only to changes in the nutrient availability but also to changes in the distribution of co-existing species. These changes can lead to an immigration of some species and a restriction of others - especially mosses and lichens.